Incidence Trends for Papillary Thyroid Carcinoma and Their Correlation with Thyroid Surgery and Thyroid Fine-Needle Aspirate Cytology

CONTEXT: Papillary thyroid carcinoma (PTC) is the most prevalent endocrine malignancy. The reported incidence of PTC has more than doubled in many countries during the past half century. In Tasmania, an island state of the Commonwealth of Australia the incidence has increased by 24.7% per annum during the last two decades. OBJECTIVE: Using the Tasmanian population as a model, this study sought to determine the relationship between changes in PTC incidence and trends for utilization of thyroid surgery and thyroid fine-needle aspiration biopsy (FNAB) cytology. DESIGN: Hospital and pathology services in Tasmania provided data relating to all thyroid surgical, cytologic, and histopathology procedures undertaken between 1988 and 1998. The accuracy of PTC case ascertainment by the Tasmanian Cancer Registry was validated and the relationship between thyroid procedures and PTC incidence assessed. RESULTS: A total of 3452 individuals underwent a thyroid procedure, comprising 1968 surgical and 1756 FNAB cytologic procedures. Of these, 184 patients were diagnosed with thyroid carcinoma, of whom 121 (65.8%) had PTC. Thyroidectomy and thyroid FNAB increased by 7.0% and 49.7% per annum, respectively. The likelihood of diagnosing PTC in thyroidectomy specimens increased by 99.7% per year in those patients preoperatively assessed by FNAB, compared to 10.1% per year in those for whom a preoperative FNAB was not performed. PTC incidence increased independently of PTC tumor size, although the greatest increase occurred for PTC 1 cm or less with a history of preoperative FNAB. CONCLUSIONS: These results suggest increasing PTC incidence is largely attributable to greater diagnosis of small PTC, many of which are likely to have been asymptomatic, identified by neck ultrasonography and subsequent FNAB. However, the incidence of PTC larger than 1 cm in patients without history of preoperative FNAB has also risen, suggesting the occurrence of clinically relevant tumors may also have increased.